1. Field of the Invention.
This invention relates to frequency-hopping communication systems for wireless data communication of digitized voice signals.
2. Prior Art.
The use of frequency-hopping radio systems for wireless data communication has become prevalent because of the FCC rules governing unlicensed operation in the Industrial, Scientific, and Medical (ISM) bands. Unfortunately, because of the loosely regulated nature of these bands, there is a high likelihood that radio systems operating in these ISM bands will interfere with each other. Interference from other radio systems operating in these bands along with various other transmission impairments, such as multipath fading, make it difficult for these radio systems to obtain bit error rates that are low enough to provide useful communication services, particularly for digital transmission of voice signals.
One technique for overcoming these shortcomings for the ISM bands for asynchronous data traffic is an Automatic Retry Request (ARQ) error correction technique. With ARQ, the data information to be sent from a source transmitter to a destination receiver is broken up into smaller packets. Each of these smaller data packets is then sent from the source to the destination over a single radio-frequency channel. If an entire data packet is received correctly by the destination, the destination sends a positive acknowledgment signal back to the source. The source then sends the next data packet on a different radio channel and the acknowledgment process is repeated. If the destination receives a data packet with errors, the destination can either not reply with an acknowledgment signal or reply with a negative acknowledgment signal. In either case, the source then retransmits the data packet that was received in error on yet another radio frequency. This process is repeated until a data packet is received without errors and the source receives a positive acknowledgment.
With this ARQ retransmission/acknowledgment technique, all of the data packets comprising the original information are sent as many times as is necessary for error free reception. Note that, while the ARQ technique provides very low error rates, the ARQ technique cannot guarantee the maximum amount of time required to send the information correctly.
For digital transmission of voice signals, much higher error rates can be tolerated than those required for the reliable transmission of data. However, transmission of voice signals require that the communication channel guarantee a minimum information throughput and a maximum amount of delay time. The voice signals must be sent in near-real time without any major interruptions or time gaps to provide intelligible and satisfactory reproduction of the voice signals.